Most of the gas molecules in our atmosphere are nitrogen (N2) and oxygen (O2). Each of these types of molecules has just two atoms. This means these molecules can only vibrate in one way, and therefore aren't very good at absorbing energy. Carbon dioxide (CO2) and water vapor (H2O) molecules, on the other hand, have three atoms per molecule... so they can vibrate in various different ways. This makes them better at absorbing energy from infrared radiation... which is why they are such effective greenhouse gases.

Adding extra carbon dioxide to Earth's atmosphere increases the temperature of the atmosphere. Humans have added lots of CO2 to the atmosphere, mostly by burning fossil fuels such as oil, coal, and natural gas. This extra CO2 enhances the greenhouse effect and is the main cause of global warming.

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